Department of Hematology/Oncology, Johann Wolfgang Goethe University, 60590 Frankfurt, Germany.
Department of Microbiology-Immunology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611.
Proc Natl Acad Sci U S A. 2020 Oct 20;117(42):26318-26327. doi: 10.1073/pnas.2007946117. Epub 2020 Oct 5.
Epstein-Barr virus (EBV) infects human B cells and reprograms them to allow virus replication and persistence. One key viral factor in this process is latent membrane protein 2A (LMP2A), which has been described as a B cell receptor (BCR) mimic promoting malignant transformation. However, how LMP2A signaling contributes to tumorigenesis remains elusive. By comparing LMP2A and BCR signaling in primary human B cells using phosphoproteomics and transcriptome profiling, we identified molecular mechanisms through which LMP2A affects B cell biology. Consistent with the literature, we found that LMP2A mimics a subset of BCR signaling events, including tyrosine phosphorylation of the kinase SYK, the calcium initiation complex consisting of BLNK, BTK, and PLCγ2, and its downstream transcription factor NFAT. However, the majority of LMP2A-induced signaling events markedly differed from those induced by BCR stimulation. These included differential phosphorylation of kinases, phosphatases, adaptor proteins, transcription factors such as nuclear factor κB (NF-κB) and TCF3, as well as widespread changes in the transcriptional output of LMP2A-expressing B cells. LMP2A affected apoptosis and cell-cycle checkpoints by dysregulating the expression of apoptosis regulators such as BCl-xL and the tumor suppressor retinoblastoma-associated protein 1 (RB1). LMP2A cooperated with MYC and mutant cyclin D3, two oncogenic drivers of Burkitt lymphoma, to promote proliferation and survival of primary human B cells by counteracting MYC-induced apoptosis and by inhibiting RB1 function, thereby promoting cell-cycle progression. Our results indicate that LMP2A is not a pure BCR mimic but rather rewires intracellular signaling in EBV-infected B cells that optimizes cell survival and proliferation, setting the stage for oncogenic transformation.
爱泼斯坦-巴尔病毒（EBV）感染人类 B 细胞，并对其进行重编程以允许病毒复制和持续存在。在这个过程中，一个关键的病毒因子是潜伏膜蛋白 2A（LMP2A），它被描述为促进恶性转化的 B 细胞受体（BCR）模拟物。然而，LMP2A 信号如何促进肿瘤发生仍然难以捉摸。通过使用磷酸化蛋白质组学和转录组谱比较 LMP2A 和 BCR 在原代人 B 细胞中的信号，我们确定了 LMP2A 影响 B 细胞生物学的分子机制。与文献一致，我们发现 LMP2A 模拟了 BCR 信号事件的一部分，包括激酶 SYK 的酪氨酸磷酸化、由 BLNK、BTK 和 PLCγ2 组成的钙起始复合物及其下游转录因子 NFAT。然而，LMP2A 诱导的大多数信号事件与 BCR 刺激诱导的信号事件明显不同。这些包括激酶、磷酸酶、衔接蛋白、转录因子（如核因子 κB（NF-κB）和 TCF3）的差异磷酸化，以及 LMP2A 表达的 B 细胞转录输出的广泛变化。LMP2A 通过失调凋亡调节剂如 BCl-xL 和肿瘤抑制因子视网膜母细胞瘤相关蛋白 1（RB1）的表达来影响细胞凋亡和细胞周期检查点。LMP2A 与 MYC 和突变型 cyclin D3 合作，通过抵消 MYC 诱导的凋亡和抑制 RB1 功能，促进原代人 B 细胞的增殖和存活，这两种都是 Burkitt 淋巴瘤的致癌驱动因素，从而促进细胞周期进程。我们的研究结果表明，LMP2A 不是纯 BCR 模拟物，而是重新布线 EBV 感染的 B 细胞中的细胞内信号，优化细胞存活和增殖，为致癌转化奠定基础。
